Bob's Knobs

[CSM]

Having read all the comments on these I bought a set for my Celestron NexStar 6SE - I am a bit of a fiddler and always seeking to get that bit extra out of my scope.  And having fitted them and collimated the scope I thought it all looked good.  However, the next time, last night, after realigning the scope, the rings were anything but concentric and reading on the Starizona website the following.

Note:  In our experience, the original screws on an SCT secondary mirror are much better to use for collimation purposes than the aftermarket thumbscrews that can be added.  Thumbscrews cannot be turned as precisely, making accurate alignment difficult.  Also, thumbscrews do not hold the mirror as tightly, increasing the need to collimate more often.  Thumbscrews also tend to make people "collimation happy," tending to collimate a scope far more often than necessary.  Under normal use, you should be able to go months without collimating a telescope.

Which is what seems to have happened to me.  Anyone any thoughts or suggestions about this?

[rowan46]

It's a valid opinion but having used bob's knobs I find the much less stressful than trying to turn a screw in the dark whilst looking down an eyepiece and turtling about with a sharp instrument near my corrector plate.

[ChrisLX200]

Having read all the comments on these I bought a set for my Celestron NexStar 6SE - I am a bit of a fiddler and always seeking to get that bit extra out of my scope.  And having fitted them and collimated the scope I thought it all looked good.  However, the next time, last night, after realigning the scope, the rings were anything but concentric and reading on the Starizona website the following.

Which is what seems to have happened to me.  Anyone any thoughts or suggestions about this?

Well that sounds rubbish to me (not putting too fine a point on it). Whilst there _are_ a few caveats that may apply in terms of quality of manufacture (of the threads) such that they fit correctly and are not loose, and the length is correct, and that the person installing them does so correctly (not leaving the secondary hanging off the last few threads of the screws)... then I can think of only good things to say about them. The argument for making it more awkward to colimate so that you don't bother to do it so often is a joke, right?

ChrisH

[Charic]

CSM.........Hi there, ..........."Under normal use, you should be able to go months without collimating a telescope."........ that's the department I'm in. Although that has struck a note with ChrisLX200! it is only your opinion  CSM, that they don't work.

If your telescope doesn't get used every night, or like me you take extreme care when handling the equipment, then collimation is not something that needs adjusting every-time (a check maybe) My scope just out of nearly 3 Months hibernation, and upon checking collimation, still  perfect, so no adjustment according to my Barlowed Laser. And the Cheshire aligns just as well.

I, like yourself have looked into the option of a tool-less environment for adjustments to the telescope. The three main reasons, I chose not to buy so-far ( for my telescope ) are, the initial expense for a few bolts, however that said, these bolts come with modified washers for the countersunk holes on the Skyliner base, so a normal nut and bolt just wont fit, without something to assist in holding the bolt in place through the frame, as it screws into the mirror cell. Secondly, I sometimes stand the OTA end-on if removed from its base, the advice is not to rest the OTA on the adjusters, for obvious reason, and reach is the last issue. I just cant reach all the adjusters and look through the eyepiece at the same time.

Maybe you can return them for a refund. Not all retailers are so obliging. Its not that they don't always work, their just not working for you on this occasion.

[CodnorPaul]

I fitted Bobs Knobs 8 months or so ago and not touched collimation since - I check it every time I use the scope but it has stayed spot on

[CSM]

Reactions as expected.  No I am not saying that they don't work or that the comment about them not being as good as the original screws is correct. However I would say that if it is true that it is based on experience, that is more than one person using them, it is more likely to be true.  It may well be that those choosing replacement screws are more inclined to worry about collimation and do it more often and it may well be that I simply got it wrong on my scope - I usually do!  Have just found the original screws but will persist with Bob's for the moment.

[Floater]

Bob's Knobs do it for me. I found the original screws very annoying.

Rowan46 says it like it is - no faffing about with a screwdriver; much easier just to tweak the setting. And my Skyliner holds colimation rock solid.

Thumbs up for thumb screws!

[andyman]

CSM.........Hi there, ..........."Under normal use, you should be able to go months without collimating a telescope."........ that's the department I'm in. Although that has struck a note with ChrisLX200! it is only your opinion  CSM, that they don't work.

If your telescope doesn't get used every night, or like me you take extreme care when handling the equipment, then collimation is not something that needs adjusting every-time (a check maybe) My scope just out of nearly 3 Months hibernation, and upon checking collimation, still  perfect, so no adjustment according to my Barlowed Laser. And the Cheshire aligns just as well.

I, like yourself have looked into the option of a tool-less environment for adjustments to the telescope. The three main reasons, I chose not to buy so-far ( for my telescope ) are, the initial expense for a few bolts, however that said, these bolts come with modified washers for the countersunk holes on the Skyliner base, so a normal nut and bolt just wont fit, without something to assist in holding the bolt in place through the frame, as it screws into the mirror cell. Secondly, I sometimes stand the OTA end-on if removed from its base, the advice is not to rest the OTA on the adjusters, for obvious reason, and reach is the last issue. I just cant reach all the adjusters and look through the eyepiece at the same time.

Maybe you can return them for a refund. Not all retailers are so obliging. Its not that they don't always work, their just not working for you on this occasion.

Unless its a flextube which require regular collimation...but even then its just a tweak.as for bobs knobs makes collimation a doddle

[Sirius Starwatcher]

Thanks for the info does this mean that I have to start another wish list putting Bobs knobs on it ?

[Mr Spock]

I use Bob's Knobs and it made collimation much easier. A small cross head screwdriver in the dark is a task for someone with more patience than me

I haven't touched the collimation since it was done...

[Stargazer33]

I bought some Bob's Knobs and found it very easy to collimate my C8. I check collimation most outings, normally when I'm changing from one ep to another, or to a camera and it is always unchanged - at least to my eyes! Like has been said before, I didn't want to be poking around the corrector plate of my SCT, in the dark, with a screwdriver!

At the end of the day though, it is what works for you as in all things.

[Northern Soul man]

I think I've collimated the 1100 only twice in the two years owning it, when I installed Bobs Knobs, I took more care in the actual initial tension of the three screws before even thinking about collimation - I found that you have to tension them up giving an even secure feeling on all of them, I found that the actual adjustment of each screw was a relative "minor" turn or so to get everything central - you get a feel for how much to tighten them to get a good overall collimation AND correct tension on each one - this gives a much more "secure" secondary and doesn't have the chance to "move " out of collimation much at all - as said, over 2 years, the scope has been in and out of my Dad's car on numerous occasions and has held collimation very well - after cool down and low power observations, I then "put" it on a star nice and high up and just check collimation in and out of focus and can say that I never have had to adjust - so initial correct tension before collimating always has worked for me - but I don't get worried about it, just use the scope and enjoy.

Regards.

Paul.

[Tinker1947]

These are not Bob's Knob's there stainless steel and cost around £5......

[Floater]

As Tinker shows, there are more economical choices. However, the same reasoning applies: it's easier to to turn a knurled knob with your fingers than to poke about with a screwdriver ...

[Dude_with_the_tube]

i dont know what size screws goes into your Celestrons,but for dobs its a simple M4x30mm thumb screw.Dont need any Bobs or Andy`s knobs for that.You can pick M4x30mm thumb screw up for as less as £1.50 per piece.Thats what i did on my 10" and the same was done on 14".Works a treat and replaces the original allen screws for very little cost.

[Charic]

i dont know what size screws goes into your Celestrons,but for dobs its a simple M4x30mm thumb screw.Dont need any Bobs or Andy`s knobs for that.You can pick M4x30mm thumb screw up for as less as £1.50 per piece.Thats what i did on my 10" and the same was done on 14".Works a treat and replaces the original allen screws for very little cost.

........Did you manage the same for the primary mirror?  On the 200P/Dob  the collimation adjusters are butted into  countersunk holes. This provides a base  for the adjusters to draw the mirror cell towards  the main housing, under  slight tension of the rubber washers. I don't see how thumbscrews can work if you don't have any nylon tube washers to fit between the countersink and the head of the thumb screw, or some sort of additional washer, unless the thumbscrew is long enough and just rests in the countersunk hole!

[Tinker1947]

I put Wing Nuts (they might be Thumb Screws ) on the Dob Secondary, makes it so easy to adjust.......

[ChrisLX200]

What started me into making these things was many years ago trying to adjust colimation on my 10" SCT with a tiny Allen key, first I poked the end into the corrector plate (followed by much cursing) then promptly dropped the key into wet grass where it was never to be seen again and doubtless resides to this day. It was difficult to turn the key with any precision anyway. So instead I made a little knurled disk with short length of hex wrench protruding and tried that. A definite improvement in terms of being able to turn the screws accurately, and inserting the thing into the hex sockets in the screws was easier than inserting the angled key, but it was still liable to be dropped. Then I removed a screw completely and wondered if I could combine the two - and the thumbscrew adjuster was born.

However, mine were made from stainless, with slightly over-size lathe cut threads (so they were a firm fit, had linear travel with no wobble, and held their position), and I made my first set with bronze bushes and bearing seats so they turned concentrically. The heads were anodised alloy with fiducial marks for reference. Having displayed this idea on my old website I got requests for sets and commenced making them. These were not cheap to make however - because the work involved was much more than in providing simple replacement screws with a 'similar' #7-32 rolled thread. 

A couple years later Bob arrived with his knobs, they were cheap and no-one could understand the difference between expensive ones and cheap ones. His business boomed to what it is today. Such is life, but the basic engineering principles remain the same - these are precision adjusters that need precision components to work correctly IMHO (or at least, better than the original screws which were nothing special to start with). They need to be long enough to use ALL the available female thread in the secondary housing for support, and the housing should be colimated with it snugged up as close to the corrector plate as possible (to prevent movement post-colimation as far as possible). With this done then yes, colimation remains stable for long periods - but it can be checked and tweaked quickly IF needed. My 10" LX200 used to get carted to a dark site in the back of my car over some rough country roads all the time, most often it survived this journey very well but the odd pothole would try its best to dislocate the secondary and this was why colimation was checked at the beginning of every session.

I used to make all sorts of crazy things - like an illuminated bubble level? Easy, just find yourself an old meniscus lens, cut a circular groove with a pointed carbide tool in the glass, fill with paint and make an oil-filled casing... with a bubble in it

ChrisH

[Floater]

Nice post, Chris.

However, your engineering skills are way ahead of mine. In fact, I have no skill in that arena - hence my purchase of Bob's Knobs.

I never cease to be impressed by what you workshop savvy guys can do.

Respect.

[rwilkey]

I tried Bob's Knobs on my 200P, and I think one of the screws had a faulty thread or something I couldn't fathom, anyway I could not get collimation, so asked a friend who is more expert than me to put the telescope right, so Bob's Knobs came out and we put the original screws back in, the telescope is now collimated.  Anyway, just thought I would share my experience, but I can see the benefits.

[Ryan P]

Hi, i'm new to the forum and have just come across this thread. I am an amateur astronomer just looking into getting my first Dobsonian Telescope. As you do i've been looking around the forums etc and one thing that keeps popping up are these Bob's Knobs. I can't actually believe how expensive and how poorly made they seem to be. They look like knurled knobs that have been locktighted onto some standard threaded bar. Im interested in all this because I am a CNC engineer by trade. I operate numerous CNC lathes, including some pretty nice ones like the Takisawa EX-308. We mass produce things like this day in day out and will be planning on making my own. However unlike Bobs Knobs I will be making mine more like Sub Dwarf did above. With the precision machined threads for a start with a much better fit! Also I think the roughness of the thread ends of the bobs knobs look awful. I was thinking of capping them with something softer but still Durable like Nylon/Polypropylene/Acetal etc. I cannot get my head around the price of these things to be fair. I suppose its a bit of a niche marked. I just know for a fact these could be made a lot cheaper and to a much better quality! 

[Dave In Vermont]

I use the Bob's for the reason that I, as has been remarked, don't want to be messing with my collimation screws with a sharp tool near the corrector-plate. However I am not a brand-loyalist. If a similar product had come along for less money, and higher quality, than the Bob's. I'd have gone for them.

So RyanP: Have you got much spare time? How about a nice, little cottage-industry?

Clear & Dark Skies,

Dave

[Ryan P]

Hi Dave, yeah they seem like a great idea. The fact you can scrap your Allen keys and just use thumbscrews is great. I would love to set up a small engineering business for making things like this. Its just so expensive to do so. It would be a gamble as to weather or not you could make enough to sustain the outlay of setting up such a business. Definitely food for thought though.

[CodnorPaul]

Hi Dave, yeah they seem like a great idea. The fact you can scrap your Allen keys and just use thumbscrews is great. I would love to set up a small engineering business for making things like this. Its just so expensive to do so. It would be a gamble as to weather or not you could make enough to sustain the outlay of setting up such a business. Definitely food for thought though.

So perhaps there is a reason for the cost he charges for the product he produces...  I use them and find them great.  Are they the highest quality - who cares they work fine for what they do which is a thumb tight adjustment of a secondary mirror, not a major load

[DRT]

I fitted Bob's Knobs to my Flextube 300P and Omni 150 Newt today and am absolutely delighted with the result. Adjustment in the dark is no longer a case of fumbling around in the grass looking for an Allen key!

A tip for those wishing to fit these to a Newt/Dob - I put my laser collimation tool in the focus tube during the procedure and replaced one screw at a time. The laser allowed me to keep the scopes close to collimation throughout the process and a small adjustment once the third screw was in place was all that was required to finish off.

I can see why people will consider these little screws expensive but I think they are good value when you consider the convenience and time saving they will provide for years to come.